The end dump fifth wheel trailer is a frameless trailer with a stabilization system that holds the kingpin plate in a generally horizontal position.
Fifth wheel trailers with end dumps have hydraulic cylinder lift systems for dumping bulk material from an open rear end gate. One of the two basic types of such trailers is referred to a frame-type trailer. The other type is referred to as a frameless-type trailer.
The frame-type end dump trailers have a trailer frame with a kingpin connectable to a fifth wheel that supports the forward end of the frame and wheels and axles that support the rear end of the frame. A cargo container is pivotally attached to the rear of the frame for pivotable movement about a horizontal axis that is transverse to the normal direction of trailer movement. At least one hydraulic cylinder is pivotally connected to the front of the frame and to the cargo container. Extension of the hydraulic cylinder pivots the cargo container about the axis of the pivot connection to the frame and lifts the front end of the cargo container relative to the trailer frame. The trailer frame remains generally horizontal and provides a somewhat stable platform for the cargo container. The trailer kingpin generally vertical and the kingpin plate which is fixed to the trailer frame and sets on the top surface of the fifth wheel remains generally horizontal. The kingpin permits pivotal movement of the trailer about a vertical axis relative to a tractor. A pivotal connection between the fifth wheel and the tractor frame permits the trailer frame to pivot about a transverse horizontal axis relative to the tractor. Without the transverse pivot connection between the fifth wheel and the tractor frame, there would be a tendency to lift the front steered wheels off the ground at times and to overload the steered wheels at other times when traveling on uneven road surfaces. This tendency to transfer weight between front and rear axles can result in tractor and trailer damage.
A major drawback of the frame-type end dump fifth wheel trailer is weight. The main frame has sufficient strength and material to support the entire weight of the cargo container and the cargo in the cargo container. When the front end of the cargo container is first raised by a hydraulic cylinder to dump cargo from the open rear end gate, the cargo container must have sufficient strength to support the weight of the cargo as well as the weight of the cargo container. The result is a trailer with excess weight and reduced cargo capacity.
The frameless-type trailer has a cargo container with rear support wheels connected directly to rear portion of the cargo container. A kingpin plate and a kingpin are pivotally attached to a hydraulic cylinder that lifts the cargo container to dump cargo. The kingpin is latched to a fifth wheel and the kingpin plate sits on the upper bearing surface of the fifth wheel. A pair of tension beams have forward ends pivotally attached to the kingpin plate and rear ends pivotally attached to a cargo container midway between the front end and the rear end of the frameless trailer. These tension beams transmit force from the kingpin to the trailer wheels to move the trailer forward and rearward. The beams also transmit force from the kingpin to the cargo container when the tractor brakes are applied.
The fifth wheel of a tractor is locked in place relative to the tractor frame when pulling a frameless trailer to hold the kingpin plate and the fifth wheel upper surface in a generally horizontal position. The pivot connection between the hydraulic cylinder, the right tension beam, and the left tension beam, and the kingpin plate all have transverse horizontal axes and permit the trailer to pivot about a transverse horizontal axis relative to the tractor when the fifth wheel is locked relative to the tractor frame.
Long cargo compartments of semi-trailers may become unstable when the cargo compartment is raised to a dump position. The maximum width of a trailer is 8.5 feet. The center of gravity prior to raising a cargo container loaded with sand or crushed rock is most likely about 7 feet above a tractor support surface. When the trailer cargo compartment is raised to a dump position the cargo in the front portion of the compartment is well over 20 feet above the trailer support surface and supported on a base that extends less than 8.5 feet in width. If the fifth wheel is not locked relative to the tractor frame, and the tractor is out of fore and aft alignment with the trailer, shifting of the unlocked fifth wheel, about the axis of its connection to the tractor frame, to a front stop or a rear stop will move the lower end of the hydraulic cylinder a few inches toward one side or the other of the trailer and may result in the trailer laying over on one side or the other. It is therefore necessary to ensure that the fifth wheel of a tractor is locked relative to the tractor frame to minimize the chance of tipping a frameless trailer on its side.
The attachment of a frame type end dump trailer or a standard cargo trailer to a tractor with a fifth wheel locked relative to the tractor frame may result in damage to the tractor frame, tractor axles, tires, wheels and suspension systems as well as to the trailer and the fifth wheel.
The end dump fifth wheel trailer has a cargo container. At least one axle with tires and wheels is secured to a rear portion of the cargo container. A kingpin is secured to a kingpin plate assembly. A hydraulic dump cylinder is pivotally attached to the cargo container and pivotally attached to the kingpin plate assembly. An elongated tension member is pivotally attached to the kingpin assembly for pivotal movement about a plate pivot pin axis and pivotally attached to the cargo container for pivotal movement about a first container pivot axis. A kingpin plate control arm has a forward end pivotally attached to the kingpin plate assembly for pivotal movement about a plate and control arm axis that is parallel to the plate pivot pin axis and spaced from the plate pivot pin axis. The kingpin plate is control arm also has a rear end pivotally attached to the cargo container for pivotal movement about a second container pivot axis that is parallel to and spaced from the first container pivot axis. The kingpin plate control arm holds a flat bottom surface of the kingpin plate assembly in a substantially horizontal position as the cargo container is moved by the hydraulic cylinder from a lowered position to a raised position.